1. Field of the Invention
This invention has relation to an electric heater which can be externally attached to a wall of the oil pan of an automobile engine or other magnetically attractable material by the use of magnetics, can be plugged into a standard household electrical outlet, for example, and can be readily or automatically removed from the engine at the time the automobile is withdrawn from its garage or other storage place.
2. Description of the Prior Art
It is well known to magnetically attach electrically energized heaters to automotive engines. See the following patents:
______________________________________ U.S. Pat. Nos. ______________________________________ 3,194,944 Papp 7/13/65 3,835,290 Peters 9/10/74 ______________________________________
It is known to fix magnetically supported automobile engine heaters to the underside of automobiles using handles. See:
______________________________________ 2,702,335 Cordis 3/15/55 3,394,243 Lee 7/23/68 ______________________________________
During the preparation of this patent application, there was an Office Action on a copending application, Ser. No. 06/375,365, filed by us on May 6, 1982. Application Ser. No. 06/375,365 is now abandoned. In that Office Action, certain specific prior art was cited. Before the earlier application was filed, a search was made on the form of the invention disclosed in that application. All of this prior art has now been taken into consideration.
A major problem with magnetically attached heaters of the prior art has been the differences in the physical properties of a heat transfer plate having high heat conductivity and an effective magnet to work to hold the heater to the object to be heated. Permanent bar magnets, such as ceramic magnets, for example, expand and contract at different rates from heat transfer plates such, for example, as aluminum. This difference is accentuated by the fact that the aluminum takes on heat and gives up heat much faster than does the ceramic magnet. Where the two have been bonded together, this difference in coefficient of expansion and in rate of heat transfer has invariably caused the more brittle magnet to break when the magnet was closely associated with an electrical heating element used to heat the heat transfer plate. To overcome this difficulty, many of the magnetically attachable heaters of the prior art resorted to using individual magnets spaced outwardly from opposite ends of the electrical heater and heat transfer plate assemblies. Several such structures are shown in the prior art cited herein.
Such structures, while fairly effective to heat large flate plate areas, are notably ineffective where the heat must be applied in a relatively small confined area such as is often encountered in using such heaters to thaw frozen radiators, water pipes, drain pipes and, for that matter, to apply heat to oil pans of today's diminutive automobile engines.
What was needed before the present invention was a magnetically attachable heater wherein substantially the entire face of a heat transfer plate can be heated to the desired temperature, and wherein the magnetic means can operate effectively from a center portion of such heat transfer plate.
Applicants, and those in privity with them, are aware of no prior art closer than that discussed or referred to above, and are aware of no prior art which anticipates the claims herein.